This invention relates generally to fusion of polyolefin pipe and more particularly concerns the integrity of the internal environment of fusion chambers used in “pipelining.”
Heat fusion joining of sticks of plastic pipe to make a pipeline normally occurs in the field at the location where the pipeline will be installed, usually outdoors in an open or remote area with no protection from the elements. The heat fusion joining process requires keeping the pipe ends, facer and heater clean and dry because, if precipitation or blowing dirt and debris contaminate the joint, the integrity and strength of the joint are compromised. Furthermore, satisfactory fusion is directly and indirectly dependent on the temperature maintained within the fusion chamber. A climate-controlled environment is desirable simply because operator comfort during the fusion process facilitates better performance. It is necessary because in some environmental conditions the fusion process is likely not to produce a satisfactory result and the fusion process should not be performed.
In some known fusion processes, the fusion machine is kept stationary and a tent or makeshift tent like structure is used to cover the fusion machine and operator. The tent must be large enough to house the fusion machine and its operators and to allow for the heater and facer of the machine to swing into and out of the pipe path. The tent has openings to allow the pipe to enter and exit and to provide an escape for engine exhaust.
In other known fusion processes, the fusion machine is moved to make each fusion joint, a process known as “pipelining.” It is not practical, however, to move the tent with the machine for each fusion operation. For “pipelining,” the fusion machine is mounted in a climate controlled cab which travels on tracks and also incorporates some pipe handling apparatus. The cab has front and rear openings to allow the pipe sticks to enter and the fused pipe string to exit the cab. These openings have hinged doors that can be closed when no pipe stick or pipeline is in the openings, but during the fusion process the pipe stick and pipeline are in their respective openings. As a result, during the critical fusion time, the doors are left open, leaving a large opening around the pipe. Since the openings are sized for the largest pipe in the pipe range that the machine can fuse, when smaller pipe is being fused the opening around the pipe is larger.
For a pipe fusion machine to operate effectively within an environmentally controlled chamber, such as the cab of a self-propelled vehicle, it is important to seal the areas surrounding each pipe stick and the assembled pipeline at their respective entry or exit passages into or from the cab. The pipe-to-cab seal must minimize heat loss or gain in the climate-controlled air of the cab in cold or hot ambient conditions and also minimize the entry of airborne dirt and other contaminants and blowing rain, snow or sleet into the cab sufficiently to satisfy minimum fused joint standards.
Since pipe fusion machines are generally capable of handling pipes within a wide range of pipe outer diameters, it is desirable that the same seal be suitable for use with pipes of any diameter within a given fusion machine's range of diameters. At the same time, however, it is also desirable that the same seal be sufficient to close the entry or exit passage so as to preserve the cabin conditions even when no pipe stick or pipeline is extended through the entry or exit passages.
In order to keep the number of operators required by and for the fusion machine and process at a minimum, and to minimize the risk of damage to the pipe sticks or pipeline by untimely insertion into the seal, it is also desirable that the seal be passive so as to open or close without further operator interaction when the pipe stick or pipeline pushes against it on entry or is discharged from it on exit.
The issues above, including adequate climate and contaminant control for both the operator and the process, cost effectiveness of the fusion equipment package and minimization of the operator's tasks in performance of the fusion process, are not fully resolved, if at all, by known stationary and “pipelining” equipment and particularly by known pipeline seals.